Day carded a bogey-free 67 to climb to eight under to be the leading Australian, seven shots off the pace.

He says he will draw on the positive memories of his dominant Players victory in 2016 as he attempts to chase down the equal-largest 36-hole deficit at Sawgrass, set by Tim Clark in 2010.

"It's always good to come back and know you've won on a golf course like this because it is tough, and the weekend changes," Day said.

The 30-year-old Day is also inspired to continue his hot streak after winning last week's US PGA Tour event in North Carolina.

"It gives you a lot of confidence knowing you can close even when you don't have your best stuff," Day said.

Day's countryman Adam Scott's 68 left him at seven under, while Marc Leishman (71) was five shots further back.

"It was really solid stuff today from tee to green; definitely my best (ball-striking) in a long time," Scott said.

"I'd like to have two more rounds in the 60s and see where that leaves me after 72 holes because I think the course is going to firm up; I don't think (officials) want 25 under winning the tournament."